Liquid cooling system and method for cooling at least one heat generating component

ABSTRACT

A liquid cooling system for cooling at least one heat generating component, comprises a liquid loop in which liquid is arranged to be circulated, and arranged to be cooled by a first stage cooling unit, where the cold side of at least one Thermo Electric Cooling unit is arranged at a position situated downstream of the first stage cooling unit and upstream of the at least one heat generating component to be cooled by liquid, where the at least one Thermo Electric Cooling unit is arranged in its operative state to cool the liquid in order to provide for further cooling power when the cooling power of the first stage cooling unit is not sufficient.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/EP2012/051938, filed on Feb. 6, 2012, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present application relates to a liquid cooling system. The application also relates to a method for cooling at least one heat generating component.

BACKGROUND

Cooling systems are used for cooling purposes in different applications, such as e.g. for cooling components such as printed circuit boards (PCBs) or chips or memory units or Power Amplifiers, etc. in telecom base station system equipment.

A component to be cooled such as a PCB may be cooled using a heat sink by placing the component to be cooled against the heat sink base in order to be able to transfer heat from the component to the heat sink.

If more cooling power is needed, it is possible to arrange forced cooling of the heat sink, e.g., to arrange a fan that forces a flow of air across the surfaces of the heat sink cooling fins thereby replacing the air around the cooling fins which air has been heated by the heat from the cooling fins with cooler ambient air from the outside of the heat sink.

Due to the often limited base area of a component such as, for example, a PCB or a chip within the field of telecom technology and the desire to place more and more functionality on a defined base area of a component, more powerful components are developed. This increase in component capacity may be accomplished by building higher integration components. This increase in component capacity leads to that more power may be fed to components per component base area than before which in turn results in that the components emit more heat per base area than before when in maximum use during peak traffic in telecom base station systems, i.e. the maximum heat load of components is increasing as they may be fed with more power per square centimetre (W/cm2) base area.

When forced cooling with air of a heat sink placed with its base against the component to be cooled is insufficient to cool components, other methods have to be used, such as liquid cooling.

Normally, a liquid cooling system comprises one loop, e.g., a one stage loop system having only a first stage loop. The liquid in the loop is circulated therein by a pump, where further the liquid is cooled by forced cooling by that the liquid in the loop flows through a heat sink with cooling fins which cooling fins are cooled by a forced flow of ambient air on the outside of the cooling fins, where further the liquid in the loop is heated by heat from at least one heat generating component.

In a one stage loop cooling system of the above type, it is not possible to cool down the liquid to below the temperature of the ambient air. In order to be able to cool the liquid to a temperature below the ambient air, a refrigeration chiller is needed.

One possibility to realise a refrigeration chiller is by replacing the pump with a compressor where the compressor is arranged downstream of the heat sink and upstream of the component to be cooled whereby it is possible to cool the liquid to a temperature below the ambient air before the liquid reaches to component to be cooled thereby increasing the cooling of the component to be cooled. A drawback with using a compressor is that a compressor has a lower “mean time between failure (MTBF) than a pump.

Another possibility to realise a refrigeration chiller is by keeping the pump in the above mentioned one stage loop system and to add a Thermo Electric Cooling unit (TEC) downstream of the heat sink and upstream of the component to be cooled whereby it is possible to cool the liquid to a temperature below the ambient air before the liquid reaches to component to be cooled thereby increasing the cooling of the component to be cooled. A drawback is that the TEC needs to be in operation all the time even if the extra cooling power that the TEC provides is not needed to cool the component to be cooled. Another drawback is that one TEC is required for each component to be cooled. If two components are to be cooled then two TECs are needed where both have to be in operation all the time.

Another possibility, if more cooling is needed to cool down the liquid to a temperature below the ambient air before the liquid reaches to component to be cooled, is to use a two stage loop system instead of a one stage loop system, e.g., using a system having two separated liquid loops. There are some ways to realise a two stage loop system. A two stage loop system comprises a first stage liquid loop arranged to pass the component to be cooled and a second stage liquid loop arranged to pass the heat sink. The liquid in the second stage loop is circulated therein by a pump, where further the second stage liquid is cooled by forced cooling by that the second stage liquid flows within a heat sink with cooling fins which are cooled by a forced air flow of ambient air on the outside of the cooling fins, and where further the second stage liquid is heated by heat from the liquid in the first stage liquid loop by that the liquids in both loops pass through a Thermo Electric Cooling unit (TEC). The TEC is arranged to cool the first stage liquid by that the hot side of the TEC is connected to the second stage liquid loop and the cold side of the TEC is connected to the first stage liquid loop. Thus, the first stage liquid is cooled when passing the TEC, where further the first stage liquid is arranged to pass through a cold plate arranged against the component to be cooled whereby heat is transferred from the component to the cold plate and the first stage liquid, the component thereby being cooled by the first stage liquid and the first stage liquid thereby being heated by the component, whereby it is possible to cool down the first stage liquid in the above cooling system to below the temperature of the ambient air thereby increasing the cooling of the component to be cooled. No compressor is needed according to this solution. A drawback is that the TEC has to be switched on even on occasions when it is not needed to cool down the first stage liquid in the above cooling system to below the temperature of the ambient air thus resulting in unnecessary power consumption.

United States Patent Application Publication No. 2003/088538 A1 shows another type of two-stage cooling system including thermoelectric modules.

SUMMARY

The object of the present application is to provide an improved liquid cooling system and an improved method for cooling at least one heat generating component.

The object is achieved by arranging a liquid cooling system for cooling at least one heat generating component, where the liquid cooling system comprises a liquid loop in which liquid is arranged to be circulated, where the liquid is arranged to be cooled by a first stage cooling unit of the liquid cooling system, where the cold side of at least one Thermo Electric Cooling unit is arranged at a position situated downstream of the first stage cooling unit and upstream of the at least one heat generating component to be cooled by liquid, where the at least one Thermo Electric Cooling unit is arranged in its operative state to cool the liquid in order to provide for further cooling power when the cooling power of the first stage cooling unit is not sufficient, where the liquid is further arranged to cool down the hot side of the at least one Thermo Electric Cooling unit and to transfer heat generated by the at least one Thermo Electric Cooling unit to the first stage cooling unit arranged to transfer away heat from the liquid.

The object is further achieved by a method for cooling at least one heat generating component using an liquid cooling system comprising a liquid loop in which liquid is arranged to be circulated comprising the steps of, arranging the liquid to be cooled by a first stage cooling unit of the liquid cooling system, arranging at least the cold side of one Thermo Electric Cooling unit at a position situated downstream of the first stage cooling unit and upstream of the at least one heat generating component to be cooled by liquid, arranging the at least one Thermo Electric Cooling unit in its operative state to cool the liquid in order to provide for further cooling power when the cooling power of the first stage cooling unit is not sufficient, further comprising the steps of arranging the liquid to cool down the hot side of the at least one Thermo Electric Cooling unit, and transferring heat generated by the at least one Thermo Electric Cooling unit to the first stage cooling unit arranged to transfer away heat from the liquid.

By arranging a liquid cooling system with a liquid loop in which liquid is arranged to be circulated where the liquid is arranged to cool down the hot side of the at least one Thermo Electric Cooling unit and to transfer heat generated by the at least one Thermo Electric Cooling unit to the first stage cooling unit arranged to transfer away heat from the liquid, the liquid arranged for cooling of the at least one heat generating component may further be used to cool down the hot side of the at least one Thermo Electric Cooling unit and to transfer the heat generated by the at least one Thermo Electric Cooling unit away from the space surrounding the Thermo Electric Cooling unit and away from the liquid cooling system at the first stage cooling unit. This is advantageous as the Thermo Electric Cooling unit thus can be arranged in a cramped space which is sensitive to overheating whereas the first stage cooling unit may be arranged at a position where more space is available and which is not sensitive to heat emission thus allowing for more freedom in design of the placing of the second stage cooling unit, i.e. the Thermo Electric Cooling unit. A further advantage is that no additional liquid loops have to be arranged in order to cool down the hot side of the Thermo Electric Cooling unit.

By, in a liquid cooling system with a liquid loop in which liquid is arranged to be circulated, arranging the cold side of a Thermo Electric Cooling unit at a position situated downstream of the first stage cooling unit and upstream of the at least one heat generating component to be cooled by liquid, it is possible to decrease the temperature of the liquid in liquid loop to below the temperature of the liquid leaving the first cooling unit.

By, in a liquid cooling system with a liquid loop in which liquid is arranged to be circulated, arranging the cold side of a Thermo Electric Cooling unit at a position situated downstream of the first stage cooling unit and upstream of the at least one heat generating component to be cooled by liquid, it is possible to decrease the temperature of the liquid in the liquid loop to below the ambient temperature without adding a compressor to the loop which enables longer MTBF when a refrigeration function is be integrated into a liquid cooling system as no moving parts have to be added. Further, a Thermo Electric Cooling unit may also be of a flexible shape whereby it may be arranged in cramped spaces.

By, in a liquid cooling system with a liquid loop in which liquid is arranged to be circulated, arranging the cold side of a Thermo Electric Cooling unit at a position situated downstream of the first stage cooling unit and upstream of the at least one heat generating component to be cooled by liquid, it is possible to only necessitate operation of the Thermo Electric Cooling unit when additional cooling is needed.

According to one embodiment of the application, the liquid cooling system comprises a pump arranged to circulate the liquid in the liquid loop.

According to one embodiment of the application, the liquid cooling system comprises a cold plate arranged in thermal contact with both the at least one heat generating component to be cooled and the liquid.

According to one embodiment of the application, the cold side of the at least one Thermo Electric Cooling unit is arranged in thermal contact with the liquid at the said position situated downstream of the first stage cooling unit and upstream of the at least one heat generating component to be cooled.

According to one embodiment of the application, the liquid cooling system comprises a cold plate in thermal contact with both the cold side of the at least one Thermo Electric Cooling unit and the liquid.

According to one embodiment of the application, the hot side of the at least one Thermo Electric Cooling unit is arranged in thermal contact with the liquid.

According to one embodiment of the application, the liquid cooling system comprises a cold plate in thermal contact with both the hot side of the at least one Thermo Electric Cooling unit and the liquid.

According to one embodiment of the application, the hot side of the at least one Thermo Electric Cooling unit is arranged in thermal contact with the liquid at a position downstream of the last of the at least one heat generating components to be cooled.

According to one embodiment of the application, the at least one heat generating component to be cooled is a chip.

According to one embodiment of the application, the liquid cooling system comprises at least one liquid bypass arranged in the liquid loop, where the at least one liquid bypass is arranged in parallel with the at least one Thermo

Electric Cooling unit (TEC) in the loop to allow at least a part of the liquid flowing from the first stage cooling unit to the at least one heat generating component to be cooled to bypass the at least one Thermo Electric Cooling unit without coming into thermal contact with the cold side of the at least one Thermo Electric Cooling unit.

According to one embodiment of the application, the liquid cooling system comprises at least one flow control device arranged in the at least one bypass, thereby enabling control of the amount of liquid bypassing the Thermo Electric Cooling unit.

According to one embodiment of the application, the liquid cooling system comprises a control unit arranged to control at least one flow control device in at least one liquid bypass and/or to control the voltage over at least one Thermo Electric Cooling unit in order to control the temperature of the liquid arranged to cool the at least one heat generating component to be cooled.

According to one embodiment of the application, the comprising at least one liquid bypass arranged in the liquid loop, where the at least one liquid bypass is arranged in parallel with the at least one Thermo Electric Cooling unit (TEC) in the loop to allow at least a part of the liquid flowing from the at least one heat generating component to be cooled to the at least one first stage cooling unit to bypass the at least one Thermo Electric Cooling unit without coming into thermal contact with the hot side of the at least one Thermo Electric Cooling unit.

Further advantages of the application will be apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended drawings are intended to clarify and explain different embodiments of the present application in which:

FIG. 1 shows a schematic diagram of a prior art two-stage liquid cooling system design;

FIG. 2 shows a schematic diagram of a liquid cooling system according to a first embodiment of the application, and

FIG. 3 shows a schematic diagram of a liquid cooling system according to a second embodiment of the application.

DETAILED DESCRIPTION

In connection with this description, the word “liquid” refers to fluids such as water, glycol, etc. and mixtures of these fluids (e.g., a mixture comprising both water and glycol).

FIG. 1 shows a schematic diagram of a prior art two-stage liquid cooling system 1. The two-stage liquid cooling system 1 includes a first stage liquid loop 3 arranged to pass the component 5 to be cooled and a second stage liquid loop 7 arranged to pass a heat sink 9. The liquid 11 in the second stage loop 7 is circulated therein by a pump 13, where further the second stage liquid 11 is cooled by forced cooling by that the second stage liquid 11 flows within a heat sink 9 with cooling fins 15 which are cooled by a forced air flow of ambient air 17 on the outside of the cooling fins 15, and where further the second stage liquid 11 is heated by heat from the liquid 19 in the first stage liquid loop 3 by that the liquids 11, 19 in both loops 3, 7 pass through a Thermo Electric Cooling unit (TEC) 21. The TEC 21 is arranged to cool the first stage liquid 19 by that the hot side 23 of the TEC 21 is connected to the second stage liquid loop 7 and the cold side 25 of the TEC 21 is connected to the first stage liquid loop 3. Thus, the first stage liquid 19 is cooled when passing the TEC 21, where further the first stage liquid 19 is arranged to pass through a cold plate 27 arranged against the component 5 to be cooled whereby heat is transferred from the component 5 to the cold plate 27 and the first stage liquid 19, the component 5 thereby being cooled by the first stage liquid 19 and the first stage liquid 19 thereby being heated by the component 5. By using the TEC 21, it is possible to cool down the first stage liquid 19 in the above cooling system 1 to below the temperature of the ambient air 17 thereby increasing the cooling of the component 5 to be cooled. The drawback is that the TEC 21 has to be switched on even on occasions when it is not needed to cool down the first stage liquid 19 in the above cooling system 1 to below the temperature of the ambient 17 air thus resulting in unnecessary power consumption as a TEC has relatively low efficiency.

FIG. 2 shows a schematic diagram of a liquid cooling system 2 according to a first embodiment of the application, where the liquid cooling system 2 includes a liquid loop 4 in which liquid 6 is arranged to be circulated by a pump 8. The liquid 6 is arranged to cool at least one heat generating component 10 to be cooled by liquid 6 by that the liquid 6 is arranged to cool a cold plate 12 arranged in thermal contact with the at least one heat generating component 10 to be cooled and the liquid 6, where the liquid 6 is preferably arranged to pass through the cold plate 12. Thus the at least one heat generating component 10 to be cooled is cooled by the liquid 6 by that heat is transferred from the heat generating component 10 to the cold plate 12 and the liquid 6, the liquid 6 thereby being heated by the heat generating component 10.

The liquid loop 4 includes liquid transport pathways such as conduits, hoses, channels in cold plates, etc. in which the liquid 6 is transported.

In order to cool the liquid 6, the liquid is arranged to be cooled by a first stage cooling unit 14 of the liquid cooling system 2 where the liquid 6 is preferably arranged to be cooled to ambient temperature or above, e.g., by using air 16, where further preferably the liquid 6 is cooled by a forced air flow of, preferably ambient, air 16 where the forced air flow preferably is generated by at least one fan 18. The first stage cooling unit 14 preferably includes a heat sink 20 where preferably the liquid 6 is arranged to flow through the heat sink 20 where further preferably the heat sink 20 includes cooling fins 22. The air 16 is preferably arranged to flow past the outer surface of several cooling fins 22 whereby heat is transferred from the cooling fins 22 to the flow of air 16. A heat exchanger may be used in place of the heat sink 20.

In order to provide for further cooling power for a situation where the cooling power of the first stage cooling unit 14 is not sufficient to cool the at least one heat generating component 10 to be cooled, at least one Thermo Electric Cooling unit (TEC) 24 of the liquid cooling system 2 is arranged in its operative state, i.e. when switched on, to cool the liquid 6 at a position situated downstream of the first stage cooling unit 14 and upstream of the at least one heat generating component 10 to be cooled by liquid 6, at which position the liquid 6 is arranged in thermal contact with the cold side 26 of the at least one TEC 24, where the liquid 6 is preferably arranged to pass through the cold side of the at least one TEC 24 or through a cold plate 28 in thermal contact with the cold side 26 of the at least one TEC 24 and the liquid 6, where the liquid 6 preferably is arranged to pass through at least one channel 30 arranged therein. By using a TEC 24 it is possible to cool the liquid 6 to below the ambient temperature, i.e. below the temperature of the air 16 arranged to cool the liquid 6 at the first stage cooling unit 14, whereby the liquid 6 already cooled by the first stage cooling unit 14 is further cooled by the TEC 24 before reaching the at least one heat generating component 10 to be cooled by liquid 6.

A Thermo Electric Cooling unit (TEC), also called a Peltier cooler, is a active heat pump which is arranged to transfer heat from the cold side of the device to the hot side of the device when a voltage is applied over the TEC and a current runs through the TEC. Heat is thus pumped from the cold side to the hot side using electrical energy, whereby the cold side is cooled and the hot side is heated.

Electric power is used to generate a temperature difference between the two sides of the device. By varying the voltage over the TEC 24, control of the cooling power of the TEC is achieved, the TEC 24 thereby being arranged to handle varying heat loads.

Due to the relatively low efficiency of the TEC 24, a lot of heat is generated at the hot side 32 of the device when in operation. As is shown in the figure, it is thus advantageous to arrange the loop 4 in such a way that the liquid 6, preferably after having passed the last of the at least one heat generating components 10 to be cooled by liquid 6, i.e.” downstream of the last of the at least one heat generating components 10 to be cooled by liquid 6, is arranged in thermal contact (thermally coupled) with the hot side 32 of the at least one TEC 24, where the liquid 6 is preferably arranged to pass through the hot side of the at least one TEC 24 or through a cold plate 34 in thermal contact with the hot side 32 of the at least one TEC 24 and the liquid 6, where the liquid 6 preferably is arranged to pass through at least one channel 36 arranged therein. Thus, the liquid 6 may further be used to cool down the hot side 32 of the at least one TEC 24 and to transfer the heat generated by the at least one TEC 24 away from the space surrounding the TEC 24 in order to transfer heat away from the liquid cooling system 2 at the first stage cooling unit 14 the liquid 6 thereby being heated by the hot side 32 of the at least one TEC 24. This is advantageous as the TEC 24 thus can be arranged in a cramped space which is sensitive to overheating whereas the first stage cooling unit 14 may be arranged at a position where more space is available and which is not sensitive to heat emission thus allowing for more freedom in design of the placing of the second stage cooling unit, i.e. the TEC 24. A further advantage is that no additional liquid loops have to be arranged in order to cool down the TEC 24.

Thus, the liquid cooling system 2 according to the application is arranged for cooling at least one heat generating component 10, where the liquid cooling system 2 comprises a liquid loop 4 in which liquid 6 is arranged to be circulated, where the liquid 6 is arranged to be cooled by a first stage cooling unit 14, where the cold side 26 of at least one Thermo Electric Cooling unit 24 is arranged at a position situated downstream of the first stage cooling unit 14 and upstream of the at least one heat generating component 10 to be cooled by liquid 6, where the at least one Thermo Electric Cooling unit 24 is arranged in its operative state to cool the liquid 6 in order to provide for further cooling power when the cooling power of the first stage cooling unit 14 is not sufficient, where the liquid 6 is further arranged to cool down the hot side 32 of the at least one Thermo Electric Cooling unit 24 and to transfer heat generated by the at least one Thermo Electric Cooling unit 24 to the first stage cooling unit 14 arranged to transfer away heat from the liquid 6. Thus, the major part of the heat load generated by the TEC 24 is arranged to be transferred away from the liquid cooling system 2 by the first stage cooling unit 14.

In contrast to the above in FIG. 1 described prior art liquid cooling system, the liquid cooling system 2 according to the application may be arranged having only one liquid loop 4, thereby eliminating the need for two separate liquid loops.

With the above mentioned inventive arrangement, where the at least one Thermo Electric Cooling unit (TEC) 24 is arranged to cool the liquid 6 at a position downstream of the first stage cooling unit 14 and upstream of the at least one heat generating component 10 to be cooled by liquid 6, only one TEC 24 is needed regardless of the number of positions along the loop where heat generating components 10 that are to be cooled by liquid 6 are arranged if the said TEC 24 emits enough cooling power to the liquid 6 in the loop 4. Thus, preferably only one Thermo Electric Cooling unit (TEC) 24 is arranged to cool the liquid 6 at the above mentioned position.

The at least one heat generating component 10 to be cooled by liquid 6 may be, for example, a chip, such as an integrated circuit chip, arranged on a PCB. The heat generating components 10 to be cooled by liquid 6 may be a number of chips which may be arranged at different positions on a PCB, where a number of chips share one cold plate or where at least one chip is arranged with its own dedicated cold plate.

In the above embodiment, the cold side of the TEC 24 is connected in series with the loop 4.

According to this embodiment, the TEC 24 has to be switched on only on occasions when it is needed to cool down the liquid 6 in the above cooling system 2 in order to provide for further cooling power for a situation where the cooling power of the first stage cooling unit 14 is not sufficient to cool the at least one heat generating component 10 to be cooled by liquid 6, e.g. to cool the liquid 6 to a temperature below the temperature of the ambient air 16. On the other hand, if the first stage cooling unit 14 where the liquid 6 is arranged to be cooled by air 16 provides sufficient cooling power to the liquid 6 in the loop 4, i.e. when it is not necessary to utilize the additional cooling power provided by the TEC 24 due to low load, if the heat generating component 10 to be cooled by liquid 6 emits less than maximum heat due to that it is only partly in use, when traffic in a telecom base station system is low, the TEC 24 may be switched off without blocking the first stage cooling unit 14 from cooling the liquid 6 in the loop 4, thus enabling necessary cooling while avoiding unnecessary power consumption.

FIG. 3 shows a schematic diagram of a liquid cooling system according to a second embodiment of the application, where the liquid cooling system 2 includes a liquid loop 4 in which liquid 6 is arranged to be circulated by a pump 8. The liquid 6 is arranged to cool at least one heat generating component 10 to be cooled by liquid 6 by that the liquid 6 is arranged to cool a cold plate 12 arranged in thermal contact with the at least one heat generating component 10 to be cooled and the liquid 6, where the liquid 6 is preferably arranged to pass through the cold plate 12. Thus the at least one heat generating component 10 to be cooled is cooled by the liquid 6 by that heat is transferred from the heat generating component 10 to the cold plate 12 and the liquid 6, the liquid 6 thereby being heated by the heat generating component 10.

In order to cool the liquid 6, the liquid is arranged to be cooled by a first stage cooling unit 14 of the liquid cooling system 2 where the liquid 6 is preferably arranged to be cooled to ambient temperature or above by using air 16, where further preferably the liquid 6 is cooled by a forced air flow of, preferably ambient, air 16 where the forced air flow preferably is generated by at least one fan 18. The first stage cooling unit 14 preferably includes a heat sink 20 where preferably the liquid 6 is arranged to flow through the heat sink 20 where further preferably the heat sink 20 includes cooling fins 22. The air 16 is preferably arranged to flow past the outer surface of several cooling fins 22 whereby heat is transferred from the cooling fins 22 to the said flow of air 16. A heat exchanger may be used in place of the heat sink 20.

In order to provide for further cooling power for a situation where the cooling power of the first stage cooling unit 14 is not sufficient to cool the at least one heat generating component 10 to be cooled by liquid 6, at least one Thermo Electric Cooling unit (TEC) 24 of the liquid cooling system 2 is arranged in its operative state, i.e. when switched on, to cool the liquid 6 at a position situated downstream of the first stage cooling unit 14 and upstream of the at least one heat generating component 10 to be cooled by liquid 6, at which position the liquid 6 is arranged in thermal contact with the cold side 26 of the at least one TEC 24, where the liquid 6 is preferably arranged to pass through the cold side of the at least one TEC 24 or through a cold plate 28 in thermal contact with the cold side 26 of the at least one TEC 24 and the liquid 6, where the liquid 6 preferably is arranged to pass through at least one channel 30 arranged therein. By using a TEC 24 it is possible to cool the liquid 6 to below the ambient temperature, i.e. below the temperature of the air 16 arranged to cool the liquid 6 at the first stage cooling unit 14, whereby the already by the first stage cooling unit 14 cooled liquid 6 is further cooled by the TEC 24 before reaching the at least one heat generating component 10 to be cooled by liquid 6.

A Thermo Electric Cooling unit (TEC), also called a Peltier cooler, is a active heat pump which is arranged to transfer heat from the cold side of the device to the hot side of the device when a voltage is applied over the TEC and a current runs through the TEC. Heat is thus pumped from the cold side to the hot side using electrical energy, whereby the cold side is cooled and the hot side is heated.

Electric power is used to generate a temperature difference between the two sides of the device. By varying the voltage over the TEC 24, control of the cooling power of the TEC is achieved, the TEC 24 thereby being arranged to handle varying heat loads.

According to this embodiment, at least one liquid bypass is arranged in the liquid loop 4, where the at least one liquid bypass 38 is arranged to allow at least a part 40 of the liquid 6 flowing from the first stage cooling unit 14 to the at least one heat generating component 10 to be cooled by liquid 6 to bypass the at least one Thermo Electric Cooling unit (TEC) 24 arranged downstream of the first stage cooling unit 14 and upstream of the at least one heat generating component 10 to be cooled without coming into thermal contact with the cold side 26 of the at least one TEC 24. Thus, the at least one liquid bypass 38 is arranged in parallel with the at least one Thermo Electric Cooling unit (TEC) 24 in the loop.

Preferably, at least one flow control device 42 such as a valve is arranged in the at least one bypass 38, thereby enabling control of the amount of liquid bypassing the TEC 24 thereby allowing for further control of the temperature T of the liquid arranged to cool the heat generating component 10 to be cooled.

Due to the relatively low efficiency of the TEC, a lot of heat is generated at the hot side 32 of the device when in operation. As is shown in the figure, it is thus advantageous to arrange the loop 4 in such a way that the liquid 6, preferably after having passed the last of the at least one heat generating components 10 to be cooled by liquid 6, i.e. downstream of the last of the at least one heat generating components 10 to be cooled by liquid 6, is arranged in thermal contact, i.e. is arranged thermally coupled, with the hot side 32 of the at least one TEC 24, where the liquid 6 is preferably arranged to pass through the hot side of the at least one TEC 24 or through a cold plate 34 in thermal contact with both the hot side 32 of the at least one TEC 24 and the liquid 6, where the liquid 6 preferably is arranged to pass through at least one channel 36 arranged therein. Thus, the liquid 6 may further be used to cool down the hot side 32 of the at least one TEC 24 and to transfer the heat generated by the at least one TEC 24 away from the space surrounding the TEC 24 in order to transfer heat away from the liquid cooling system 2 at the first stage cooling unit 14 the liquid 6 thereby being heated by the hot side 32 of the at least one TEC 24. This is advantageous as the TEC 24 thus can be arranged in a cramped space which is sensitive to overheating whereas the first stage cooling unit 14 may be arranged at a position where more space is available and which is not sensitive to heat emission thus allowing for more freedom in design of the placing of the second stage cooling unit, i.e. the TEC 24. A further advantage is that no additional liquid loops have to be arranged in order to cool down the TEC 24.

Thus, the liquid cooling system 2 according to the application is arranged for cooling at least one heat generating component 10, where the liquid cooling system 2 includes a liquid loop 4 in which liquid 6 is arranged to be circulated, where the liquid 6 is arranged to be cooled by a first stage cooling unit 14, where at least one Thermo Electric Cooling unit is arranged at a position situated downstream of the first stage cooling unit 14 and upstream of the at least one heat generating component 10 to be cooled by liquid 6, where the at least one Thermo Electric Cooling unit 24 is arranged in its operative state to cool the liquid 6 in order to provide for further cooling power when the cooling power of the first stage cooling unit 14 is not sufficient, where the liquid 6 is further arranged to cool down the hot side 32 of the at least one Thermo Electric Cooling unit 24 and to transfer heat generated by the at least one Thermo Electric Cooling unit 24 to the first stage cooling unit 14 arranged to transfer away heat from the liquid 6. Thus, the major part of the heat load generated by the TEC 24 is arranged to be transferred away from the liquid cooling system 2 by the first stage cooling unit 14.

In contrast to the above in FIG. 1 described prior art liquid cooling system, the liquid cooling system 2 according to the application may be arranged having only one liquid loop 4, thereby eliminating the need for two separate liquid loops.

Similar to the at least one liquid bypass 38 above, further at least one further liquid bypass 44 is arranged in the liquid loop 4 according to this embodiment, where the at least one liquid bypass 44 is arranged to allow at least a part 46 of the liquid 6 flowing from the at least one heat generating component 10 to be cooled to the at least one first stage cooling unit 14 to bypass Thermo Electric Cooling unit (TEC) 24 arranged upstream of the first stage cooling unit 14 and downstream of the at least one heat generating component 10 to be cooled without coming into thermal contact with the hot side 26 of the at least one TEC 24. Thus, the at least one further liquid bypass 44 is arranged in parallel with the at least one Thermo Electric Cooling unit (TEC) 24 in the loop 4.

Preferably, at least one flow control device 48 such as a valve is arranged in the at least one further bypass 44, thereby enabling control of the amount of liquid 48 bypassing the TEC 24, in order to optimize the volume liquid flow coming into thermal contact with the hot side 32 of the at least one TEC 24 depending on if such thermal contact between the hot side 32 of the at least one TEC 24 and the liquid 6 in the loop 4 is advantageous or not. Such thermal contact would be disadvantageous if the liquid 6 at the position A is colder than the hot side 32 of the at least one TEC 24 without the liquid 6 at the position A being needed for cooling down the hot side 32 of the at least one TEC 24 the liquid 6 thereby being heated unnecessarily by the hot side 32 of the at least one TEC 24 before entering the first stage cooling unit 14.

With the above mentioned arrangement, where the at least one Thermo Electric Cooling unit (TEC) 24 is arranged to cool the liquid 6 at a position downstream of the first stage cooling unit 14 and upstream of the at least one heat generating component 10 to be cooled by liquid 6, only one TEC 24 is needed regardless of the number of positions along the loop where heat generating components 10 that are to be cooled by liquid 6 are arranged if the said TEC 24 emits enough cooling power to the liquid 6 in the loop 4. Thus, preferably only one Thermo Electric Cooling unit (TEC) 24 is arranged to cool the liquid 6 at the above mentioned position.

The at least one heat generating component 10 to be cooled by liquid 6 may e.g. be a chip which may e.g. be arranged on a PCB. The heat generating components 10 to be cooled by liquid 6 may e.g. be a number of chips which may e.g. be arranged at different positions on a PCB, where a number of chips share one cold plate or where at least one chip is arranged with its own dedicated cold plate.

According to this embodiment, the TEC 24 has to be switched on only on occasions when it is needed to cool down the liquid 6 in the above cooling system 2 in order to provide for further cooling power for a situation where the cooling power of the first stage cooling unit 14 is not sufficient to cool the at least one heat generating component 10 to be cooled by liquid 6, e.g. to cool the liquid 6 to a temperature below the temperature of the ambient air 16. On the other hand, if the first stage cooling unit 14 where the liquid 6 is arranged to be cooled by e.g. air 16 provides sufficient cooling power to the liquid 6 in the loop 4, i.e. when it is not necessary to utilize the additional cooling power provided by the TEC 24 e.g. due to low load, e.g. if the heat generating component 10 to be cooled by liquid 6 emits less than maximum heat due to that it is only partly in use e.g. when traffic in a telecom base station system is low, the TEC 24 may be switched off without blocking the first stage cooling unit 14 from cooling the liquid 6 in the loop 4, thus enabling necessary cooling while avoiding unnecessary power consumption.

A control unit 50 may be arranged to control the at least one flow control device 42, 48 in the at least one liquid bypass 38, 44 and/or to control the voltage V over the at least one TEC in order to control the temperature T of the liquid 6 arranged to cool the at least one heat generating component 10 to be cooled.

The application also relates to a method for cooling at least one heat generating component 10 using an liquid cooling system 2 comprising a liquid loop 4 in which liquid 6 is arranged to be circulated, arranging the liquid 6 to be cooled by a first stage cooling unit 14 of the liquid cooling system 2, arranging the cold side 26 of at least one Thermo Electric Cooling unit 24 at a position situated downstream of the first stage cooling unit 14 and upstream of the at least one heat generating component 10 to be cooled by liquid 6, arranging the at least one Thermo Electric Cooling unit 24 in its operative state to cool the liquid 6 in order to provide for further cooling power when the cooling power of the first stage cooling unit 14 is not sufficient, further arranging the liquid 6 to cool down the hot side 32 of the at least one Thermo Electric Cooling unit 24 and to transfer heat generated by the at least one Thermo Electric Cooling unit 24 to the first stage cooling unit 14 arranged to transfer away heat from the liquid 6.

The step of cooling at least one heat generating component 10 using an liquid cooling system 2 including a liquid loop 4 in which liquid 6 is arranged to be circulated may include the step of arranging a cold plate 12 in thermal contact with both the at least one heat generating component 10 to be cooled and the liquid 6.

The step of arranging the at least one Thermo Electric Cooling unit 24 in its operative state to cool the liquid 6 may include the steps of arranging a cold plate 28 in thermal contact with both the cold side 26 of the at least one Thermo Electric Cooling unit 24 and the liquid 6.

The step of arranging the liquid 6 to cool down the hot side 32 of the at least one Thermo Electric Cooling unit 24 may include the step of arranging a cold plate 34 in thermal contact with both the hot side 32 of the at least one Thermo Electric Cooling unit 24 and the liquid 6.

The present application is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claim. Thus, it is possible to combine features from the embodiments described above as long as the combinations are possible. 

What is claimed is:
 1. A liquid cooling system for cooling at least one heat generating component, the liquid cooling system comprising: a liquid loop in which liquid is arranged to be circulated, where the liquid is arranged to be cooled by a first stage cooling unit of the liquid cooling system, where the cold side of at least one Thermo Electric Cooling unit is arranged at a position situated downstream of the first stage cooling unit and upstream of the at least one heat generating component to be cooled by liquid, where the at least one Thermo Electric Cooling unit is arranged in its operative state to cool the liquid in order to provide for further cooling power when the cooling power of the first stage cooling unit is not sufficient, wherein the liquid is further arranged to cool down the hot side of the at least one Thermo Electric Cooling unit and to transfer heat generated by the at least one Thermo Electric Cooling unit to the first stage cooling unit arranged to transfer away heat from the liquid.
 2. The liquid cooling system according to claim 1, further comprising a pump arranged to circulate the liquid in the liquid loop.
 3. The liquid cooling system according to claim 1, further comprising a cold plate arranged in thermal contact with both the at least one heat generating component to be cooled and the liquid.
 4. The liquid cooling system according to claim 1, wherein the first stage cooling unit is arranged to be cooled by air.
 5. The liquid cooling system according to claim 4, wherein the first stage cooling unit is arranged to be cooled by a forced flow of ambient air.
 6. The liquid cooling system according to claim 1, wherein the cold side of the at least one Thermo Electric Cooling unit is arranged in thermal contact with the liquid at the said position situated downstream of the first stage cooling unit and upstream of the at least one heat generating component to be cooled.
 7. The liquid cooling system according to claim 6, further comprising a cold plate in thermal contact with both the cold side of the at least one Thermo Electric Cooling unit and the liquid.
 8. The liquid cooling system according to claim 1, wherein the hot side of the at least one Thermo Electric Cooling unit is arranged in thermal contact with the liquid.
 9. The liquid cooling system according to claim 8, further comprising a cold plate in thermal contact with both the hot side of the at least one Thermo Electric Cooling unit and the liquid.
 10. The liquid cooling system according to claim 8, wherein the hot side of the at least one Thermo Electric Cooling unit is arranged in thermal contact with the liquid at a position downstream of the last of the at least one heat generating components to be cooled.
 11. the liquid cooling system according to claim 10, further comprising a cold plate in thermal contact with both the hot side of the at least one Thermo Electric Cooling unit and the liquid.
 12. The liquid cooling system according to claim 1, wherein the at least one heat generating component to be cooled is a chip.
 13. The liquid cooling system according to claim 1, further comprising at least one liquid bypass arranged in the liquid loop, where the at least one liquid bypass is arranged in parallel with the at least one Thermo Electric Cooling unit (TEC) in the loop to allow at least a part of the liquid flowing from the first stage cooling unit to the at least one heat generating component to be cooled to bypass the at least one Thermo Electric Cooling unit without coming into thermal contact with the cold side of the at least one Thermo Electric Cooling unit.
 14. The liquid cooling system according claim 13, further comprising at least one flow control device arranged in the at least one bypass, thereby enabling control of the amount of liquid bypassing the Thermo Electric Cooling unit.
 15. The liquid cooling system according to claim 14, further comprising a control unit arranged to control at least one flow control device in at least one liquid bypass and/or to control the voltage (V) over at least one Thermo Electric Cooling unit in order to control the temperature (T) of the liquid arranged to cool the at least one heat generating component to be cooled.
 16. The liquid cooling system according claim 1, further comprising at least one liquid bypass arranged in the liquid loop, where the at least one liquid bypass is arranged in parallel with the at least one Thermo Electric Cooling unit (TEC) in the loop to allow at least a part of the liquid flowing from the at least one heat generating component to be cooled to the at least one first stage cooling unit to bypass the at least one Thermo Electric Cooling unit without coming into thermal contact with the hot side of the at least one Thermo Electric Cooling unit.
 17. The liquid cooling system according claim 16, further comprising at least one flow control device arranged in the at least one bypass, thereby enabling control of the amount of liquid bypassing the Thermo Electric Cooling unit.
 18. The liquid cooling system according to claim 17, further comprising a control unit arranged to control at least one flow control device in at least one liquid bypass and/or to control the voltage (V) over at least one Thermo Electric Cooling unit in order to control the temperature (T) of the liquid arranged to cool the at least one heat generating component to be cooled.
 19. A method for cooling at least one heat generating component using an liquid cooling system comprising a liquid loop in which liquid is arranged to be circulated, the method comprising: arranging the liquid to be cooled by a first stage cooling unit of the liquid cooling system; arranging the cold side of at least one Thermo Electric Cooling unit at a position situated downstream of the first stage cooling unit and upstream of the at least one heat generating component to be cooled by liquid; arranging the at least one Thermo Electric Cooling unit in its operative state to cool the liquid in order to provide for further cooling power when the cooling power of the first stage cooling unit is not sufficient; arranging the liquid to cool down the hot side of the at least one Thermo Electric Cooling unit; and transferring heat generated by the at least one Thermo Electric Cooling unit to the first stage cooling unit arranged to transfer away heat from the liquid.
 20. The method for cooling at least one heat generating component according to claim 19, the method further comprising arranging a cold plate in thermal contact with both the at least one heat generating component to be cooled and the liquid.
 21. The method for cooling at least one heat generating component according to claim 19, wherein the step of arranging the at least one Thermo Electric Cooling unit in its operative state to cool the liquid comprises arranging a cold plate in thermal contact with both the cold side of the at least one Thermo Electric Cooling unit and the liquid.
 22. A method for cooling at least one heat generating component according to claim 19, wherein the step of arranging the liquid to cool down the hot side of the at least one Thermo Electric Cooling unit comprises arranging a cold plate in thermal contact with both the hot side of the at least one Thermo Electric Cooling unit and the liquid. 